Our Native Ferns and Their Allies 6th ed/Ch 2
|THE ORGANS OF THE GROWING FERN.|
|Pour bien savoir une chose, il faut en savoir les details.|
20. Every one familiar with the forest and its products must have seen the young ferns unrolling from the bud in spring and early summer. It will be noticed that the fronds are coiled from the apex to the base, and form crosiers, so called from their resemblance to the head of a bishop's staff. This method of vernation is called circinate, and is rarely found except among ferns. In the grape-ferns and adder-tongues the vernation is straight or merely inclined, thus approximating that of ordinary flowering plants.
21. Rootstock.— Ferns usually spring from an underground stem called the rootstock. This may be simple or branched, smooth or scaly, horizontal, oblique, or even vertical. In some ferns it is fine and hairlike, while in others it is very large and stout. In some cases the rootstock creeps at the surface of the ground and even rises above it, as in the variety of Dryopteris contermina which grows in Florida. In the tree ferns of warmer climates it often forms a trunk fifty feet high, bearing the fronds at the summit, when it takes the name of caudex.
22. Frond.— The aerial portion consists essentially of a leaf-stalk and blade; the former is technically called the stipe, and the latter the frond. Though these are usually distinct from each other in appearance, the stipe is sometimes wanting, and in others no distinction can be made between them. Both stipe and frond, or either one, may be glabrous (smooth), pubescent (softly hairy), hairy, woolly, or scaly; when the scales are small and somewhat appressed, the surface is said to be squamous. The careful discrimination of these hairy or scaly appendages becomes a matter of importance in distinguishing many of the species of Cheilanthes. In a few of our native ferns the under surface is covered with a white or yellow powder bearing some resemblance to flour or corn starch. For this reason a surface of this character is called farinaceous. Such is the California gold-fern or “golden back” (Gymnopteris triangularis), and several of the cloak-ferns (Notholæna), and such are the various gold and silver ferns of conservatories, including some of the richest and most beautiful in the world.
23. The frond may be simple, when it consists of a single undivided leaf, as in Phyllitis or Camptosorus; or compound, when it is divided into segments. The exquisite delicacy and the extent to which this dividing is carried in some ferns determines largely their æsthetic value.
The continuation of the stipe through a simple frond is called the midvein; through a compound frond is called the rachis, and is further distinguished as primary when the frond is much compounded. A frond is entire when the margin forms an unbroken line; when so cut as to form lobes extending half way or more to the midvein it is called pinnatifid; when these incisions extend fully to the midvein the frond is said to be simply pinnate, and the divisions are called pinnæ. When the pinnæ are cut into lobes the frond is bipinnatifid and the lobes are called segments, and when these extend to the secondary midveins it is bipinnate and the divisions are called pinnules. The secondary midvein then becomes a secondary rachis. In like manner we may have ferns that are tripinnatifid and tripinnate, quadripinnatifid and quadripinnate. The last lobes are designated ultimate segments, and the last complete divisions ultimate pinnules. All these various forms from entire to quadripinnate are abundantly represented among our native ferns.
24. In some pinnate fronds, as in the oak-fern (Phegopteris dryopteris), the lower pair of pinnæ is greatly enlarged and more compound than those above, so that the stipe appears to form three branches bearing similar and nearly equal portions. Fronds of this character are usually triangular or pentagonal in outline, and this method of branching is called ternate. It will be readily seen that this is merely a modified form of the ordinary pinnate frond. Throughout the domain of nature there is infinite variety of form and structure, and at the same time unity in plan and conformity to a few generalized types.
25. Venation.— The method of veining admits of great variation, often serving to distinguish species, and more especially the sections of the various genera. In some ferns, like most shield-ferns (Dryopteris), the veins are free — that is, arising from either side of the midvein they do not unite with any other vein. In some of these the vein is simple (not branched), in others variously forked. In many the veins repeatedly anastomose or unite together, forming a series of network or areolæ. This may be somewhat irregular, as in Onoclea; or forming a single row of areolæ next to the midvein and thence free to the margin, as in Woodwardia Virginica; or forming many uniform areolæ by the parallel transverse veinlets connecting the distinct and parallel primary veins, as in Campyloneuron phyllitidis. In case the venation does not appear when examined by reflected light, it may be brought out clearly by holding the frond between the observer and the light, and then using a lens if necessary. A few fleshy species require dissection to show the veins.